Hot melt adhesives are applied to a substrate when molten, and then placed in contact with a second substrate. The adhesive cools and hardens to form a bond between the substrates. Hot melts are widely used for industrial adhesive applications such as product assembly and packaging. The latter include case and carton sealing.
Hot melts for packaging applications such as case and carton sealing are typically composed of a polymer, a diluent or tackifier, and a wax. The wax serves several functions. Because it is low in molecular weight, it reduces viscosity. Low viscosity helps to lower application temperatures, provide cleaner processing, and also good wet out of the substrates. In addition, the wax crystallizes quickly which helps the material to harden or set quickly. Fast set speed is important for high speed production. Lastly, the wax provides temperature resistance to the final bond due to its elevated melting point.
Current used packaging adhesives comprise petroleum-derived waxes such as paraffin and microcrystalline wax. The lower molecular weight of paraffin wax, makes it the primary choice when formulating low application temperature adhesives.
Recently, due to the limited supply of paraffin wax, attention has turned to the use of natural waxes. Of the natural waxes, the lowest cost materials are based on highly hydrogenated triglycerides (Borsinger et al., U.S. Pat. No. 6,890,982 B2). The high levels of hydrogenation (low iodine values) are necessary to elevate the melting point closer to paraffin. Unfortunately, with these materials it is difficult to achieve adhesives with sufficiently high melting points and adequate set speeds.
A need continues to exist for a substitute for paraffin wax, and for hot melt adhesive formulations that do not sacrifice set speed or heat resistance. The invention fulfills this need.